Spark plug



M. INGRAM SPARK PLUG Aug. 7, 1962 Filed Jan. 28, 1960 INVENTOR MAXWELL INGRAM fllllllllllllli",

A 7' TOR/VE Y 3,043,735 SP PLUG Maxwell Ingram, Dumont, Nl., assigner to Leonard Spark Plug Co., luc., a corporation of New Jersey Filed `lan. 23, 1960, Ser. No. 5,243 2 Claims. (Cl. S13- 143) This invention relates to a spark plug device and more particularly a shielded spark plug provided with an improved electrode arrangement.

It is an object of this invention to provide a spark plug of improved construction which may be readily manufactured and assembled and in which adjustment of the parts during usage is reduced to a minimum.

It is a further object of this invention to provide a spark plug construction, whereiny an improved form of electrode arrangement is provided for producing a more effective form of spark and wherein fouling, deterioration or pre-ignition elects are reduced to a minimum if not entirely eliminated.

An additional object of this invention is to provide a spark plug arrangement of the character indicated, wherein the sparking electrodes are so arranged as to automati* cally assure the proper position of alignment during the assembly operation and wherein the `sparking gap conguration is accurately maintained during usage, thereby eliminating the necessity of readjustrnent thereof.

It is also an object of this invention to provide a spark plug with an eiiective shielding arrangement against electrical effects, as well as the physical entry of moisture or deleterious foreign matter into the interior of the plug.

Other and more specific objects of the present invention will be apparent from the following description as read in connection with the accompanying drawings and claims.

in the drawings:

FIGURE l is a perspective view of a yspark plug ernbodying the instant invention;

FIGURE 2 is a vertical section thereof;

yFIGURE 3 is a bottom view thereof;

FIGURE 4 is an enlarged View showing the shroud ground electrode; and

FIGURE 5 is a `cross-sectional view of the shroud electrode shown in FIGURE 4 in inverted position.

The spark plug comprising the present invention is illustrated in FIGURES l, 2 and 3 of the drawing and comprises a body shell 11, which is threadedly engaged with an intermediate body shield 12 and Surmounted by a shielding cover assembly 13 disengagedly carried by said intermediate shield 12. The body shell 11 forms the main supporting body for the spark plug and comprises a metallic body having a lower neck portion 14 of reduced diameter, on which threads are formed for engagement with a complementary threaded aperture in the motor block of an internal combustion engine. The lower end of said neck portion 14 is provided with a ground electrode 15, which will be more particularly hereinafter described. Body shell 11 is provided with an internal annular shoulder 16 Whereon main body insulator 17 is seated.

The principal insulation between the grounded portions of the spark plug and the high voltage portions thereof is accomplished by means of the main body insulator 17. Said insulator is formed of a ceramic or similar insulating material and is positioned within shell 11. The diameter of insulator 17 is enlarged at 18 as a result of which upper and lower shoulders 19 and 2t) respectively are formed thereon. Gasket 21 is interposed between an- 3,4%,735 Patented Aug. 7, 1962 r'ice nular shou-lder 16 of the shell and :lower shoulder 20 of the insulator. A similar gasket 22 being interposed between the upper shoulder 19 of the insulator and the lower `beveled end of the intermediate body shield 12. The insulator 17 is firmly seated by the clamping action of the threaded engagement of the lower end of intermediate shield 12 with the upper end of the body shell 11. The gaskets provide gas-tight seals, as well as heat conducting paths between the insulator and the engine `block and the shell, shield and external atmosphere. Hexago-nal surfaces 23 and 24 may advantageously be provided on the shell and shield respectively permitting these elements to be clamped tightly and the plug to be mounted on an engine block by the use of suitable tools.

Body insulator 17 is provided with an axial bore 27, a portion of which is threaded as shown at 2S and further enlarged to form cavity 26. Center electrode 2.5 is disposed within axial bore 27 and is provided with a threaded upper end for mating engagement with threads 28. The center electrode is solid throughout and of circular cross section. The upper end of said center electrode is provided with an enlarged head Z9, which seats upon the `shoulder formed at the juncture of enlarged portion 26 ot the axial bore 27 with the more restricted portion thereof. A spring retaining boss 31B projects upwardly from said enlarged head 29 and carries a helical contact spring 31.

The spark plug body assembly heretofore described iS surmounted by a shielding cover assembly designated generally by the numeral 13. The shielding cover assembly comprises an elbow-shaped body 32 of electrically insulating material, such as a phenolic or ceramic material. The vertical arm 39 ot said body 32 comprises an elongated central boss 33 which is dimensioned to lit into the enlarged portion 26 of the axial bore in the main body insulator. The boss 33 is provided with an axial bore 34, which communicates with a bore 35 in the horizontal arm 36 of said elbow-shaped body 32. An elongated contact screw 37 is threadedly engaged in bore 34 at its lower extremity and terminates in a contact screw head 3S, which abuts with the upper end of contact spring 31 and forms an electrically continuous path therewith. The upper extremity of contact screw 37 is sharply pointed so that, when said screw is initially advanced into the boss, the pointed end thereof will readily pierce the insulation of an ignition cable positioned in horizontal bore 35 and make electrical contact with the conductor portion of said cable. The Vertical arm 39 also includes a transition portion 40, which is of substantially the same external diameter as the external diameter of the metallic intermediate body shield 12 and is provided with a circumferential depending flange 41, which seats upon the upper edge of said shield 12, when the shielding cover assembly is disposed upon the spark plug body. The transition portion feti has secured thereto a depending cylindrical skirt 42, which is formed of a metallic material `and is dimensioned for a tight sliding t on the intermediate shield. The upper end of the `skirt 42 is fixedly secured to said transition portion by slitting a portion of the metal of said skirt to form tongues 43, which are deflected and bite into the material from which said elbow is formed. Flange 41 formed on the transition portion deiines a groove with the wall of 33 within which the upper end of the insulator 17 is received, so that the upper edge thereof abuts with the undersurface of the transition portion 40. From the foregoing, it will be apparent that the arrangement permits the shielding cover assembly to be removed and replaced `as a unit. The provision of the elbow-shaped cover insulator as an integral unit having horizontal and vertical arm-s forms an effective arrangement for the prevention of the formation of leakage paths and shorts, as `by the entrance of moisture for example. An effective seal is also formed with the interior of the spark plug body assembly by the mating engagement of the transition surfaces with the upper edges of the intermediate shield and the body insulator. The skirt not only completes the electrical shielding of the plug body, but `also serves as an effective barrier against the entry of moisture or foreign deleterious matter. The provision of long leakage paths is a further safeguard against the deleterious effects of any moisture which might nd its way into the plug.

The ground electrode l5 for the spark plug is in the form of a frusto-conical shroud and may be formed integrally with the body shell 11. However, it has been found more advantageous to form said electrode Ias an independent unit, which is then mounted upon the lower end surface of the body shell and secu-red in position as by welding. Ground electrode i5 is more particularly illustrated in FIGURES 3, 4 and S and comprises a generally frusto-conical shell formed of suitable sheet metallic material as by stamping. Said shell is provided with a flat peripheral flange at the base of the cone and a centrally disposed aperture 45 at the frustum thereof, the tapered wall of the frusto-conical shell is provided with a series of circumferentially arranged apertures 46. The

flange 44 of the shroud ground electrode 15 is dimensioned so that it fits into the circular recess formed by the stepped lip 47 of body shell 11 thereby permitting said shroud to be more securely attached to said shell and assuring the axial alignment of the lower terminal portion of the center electrode with the central aperture formed in the -shroud Wall. shroud ground electrode is disposed, so that its concavity faces the interior of the plug and the lower end face of the center electrode is in alignment with the outer face of the shroud ground electrode. Furthermore, the said central aperture is dimensioned so that the peripheral wall defining said aperture is spaced from the center electrode surfaces, thereby forming a sparking gap therebetween. Said gap is formed symmetrically about the surface of the central electrode and comprises `a circular sparking gap. The side Wall apertures 46 are also arranged symmetrically about said center Ielectrode and form :communication parts for the chamber defined by the frusto-conical shroud electrode 15.

The instant spark plug construction provides substantial advantages both in the characteristics of its construction and its operational capabilities. The employment of the shroud electrode having a concentric aperture facilitates the manufacture and assembly of the spark plug. The arrangement further eliminates the necessity of `adjusting the sparking air gap during usage. It has been found that, when conventional types of electrodes `are employed, the ground electrode has a tendency to straighten or distort, thereby increasing the gap spacing due to the relief of internal stresses vby reason of the heat generated by the spark. In the instant construction, the tendency to change the gap spacing is eliminated. The concentric gap is also highly advantageous, in that a radial spark is produced in a 360-degree circle. The -spark distribution results in a highly effective form of fuel ignition. The concentric gap ionizes the air within the gap and facilitates voltage breakdown, thereby producing a more intense spa-rk for rapid flame propagation. An additional eifect is to facilitate quicker starts in cold Weather with low battery voltage and poorly vaporized gas. The shroud ground electrode further presents lan enlarged ground electro-de area thereby providing for a more uniform heat distribution `and increased heat dissipation. The oxidation rate of the electrodes is thus reduced, as is gap wear and erosion -of the material, thereby resulting in considerably increased plug life. The provision of the side wall laper- It will be noted that the tures further aids in the efficient operation of the plug, since in addition to free breathing around the gap, `allowance is thus made for the intake and expulsion of gases from the shell interior. While allowing for this breathing action, the ground electrode shrouds the interior of the plug and prevents oil or gas fouling of the insulator and consequent plug failure by keeping oil and liquid gas out. This feature is of even more pronounced advantage in counection with two-cycle engines, wherein lubricating oil is mixed with the gasoline fuel. A smooth idling engine is found to result. An additional advantageous feature of the invention is that pre-ignition due to heavy loads and high speed is eliminated With this type of circular electrode, in View of the increased heat dissipation and the protection of the firing chamber from intense heat.

While I have here shownand described a preferred embodiment of my invention, it will be apparent however that this invention is not limited to this embodiment and that many changes, additions `and modifications can be made in connection therewith without departing from the spirit and scope of the invention as herein disclosed and hereinafter claimed. Having described my invention what I claim as new and desire to secure by Letters Patent is:

l. In a spark plug having a body shell, an insulator disposed within said shell, said insulator being provided with an axial bore having an enlarged portion, an intermediate body shield carried -by said shell and 4in clamping engagement with said insulator, a center electrode disposed Within said insulator having a portion extending into a portion of the enlarged portion of the bore thereof, a shielding cover for said spark plug adapted to be disengageably mounted on said intermediate body shield, said cover assembly comprising an elbow shaped body of insulating material having a horizontal portion adapted to receive an ignition cable and a vertical arm, said Vertical arm being provided with a transition portion and an elongated central boss of reduced diameter depending therelfrom adapted to be received in the enlarged portion of said insulated bore when the cover is in mounted position, a contact screw extending through said vertical arm for electrical contacting engagement with said center electrode, said screw having a portion extending into the bore of the horizontal arm for electrical contact with an ignition cable when disposed thereon, a cylindrical metal skirt secured to said transition portion within which said intermediate shield is slidably received when said cover is disposed thereon.

2. In a spark plug having a body shell, an insulator disposed within said shell, said insulator being provided with an axial bore having an enlarged portion, an intermediate body shield carried by said shell and in clamping engagement with said insulator, a center electrode disposed Within said insulator having a portion extending into a portion `of the enlarged portion of the bore thereof, a ground electrode carried by said body shell, said ground electrode comprising a frusto-conical shell, said shell being provided with a centrally disposed aperture in the frustum thereof adapted to cooperate with the central elect-rode of a spark plug to form a sparking gap therewith, the side `wall of said shell being provided with a plurality of circumferentially arranged apertures, a shielding cover for said spark plug adapted to be disengageably mounted on said intermediate body shield, said cover assembly comprising an elbow-shaped body of insulating material having a horizontal portion adapted to receive an ignition cable and a vertical arm, said vertical arm being provided with a transition portion and an elongated central boss of reduced diameter depending therefrom adapted to be received in the enlarged portion of said insulated bore when the cover is in mounted position, a contact screw extending through said vertical arm for electrical contacting engagement with said center electrode, said screw having a portion extending into the bore of the horizontal arm for electrical contact with an ignition cable when disposed thereon, Ia cylindrical met-al skirt secured to said y d transition ,portion Within which said intermediate shield 2,139,793 is sldavbly received when said cover is disposed thereon. 2,616,406

References Cited in the le of this patent 554 781 UNITED STATES PATENTS 380,744 454,310

2,096,199 Rabezzana Oct. 19, 1937 6 Benton Dec. 13, 1938 Thomas Nov. 4, 1952 FOREIGN PATENTS Canada Mar. 18, 1958 France Oct. 18, 1907 Great Britain July 11, 1935 

